I think I know what you mean & am in the same delimma. I have an ambulance with a 250 altenator & a 19# 1000/800 generator. I bought cosmetic blem 320 watt solar panels for $50 ea from the factory. I have house batteries I can charge off the alt or the generator. I don't want to park in the sun so I planned to put the solar panels on a trailer but in the end is it worth it? If I go anywhere I'll be charging the house batteries & if I don't I can run the generator for 1/2 hour a day with a charger. Rainy, cloudy day the panels don't work anyway. Get a device the charges all the batteries, bus & house but won't discharge the bus starting batteries, the make a couple kinds. I think it depends on how often you'll drive.